title: Cu(II)-reduction by Escherichia coli cells is dependent on respiratory chain components.
abstract: Copper is both an essential nutrient and a toxic element able to catalyze free radicals formation which damage lipids and proteins. Although the available copper redox species in aerobic environment is Cu(II), proteins that participate in metal homeostasis use Cu(I). With isolated Escherichia coli membranes, we have previously shown that electron flow through the respiratory chain promotes cupric ions reduction by NADH dehydrogenase-2 and quinones. Here, we determined Cu(II)-reductase activity by whole cells using strains deficient in these respiratory chain components. Measurements were done by the appearance of Cu(I) in the supernatants of cells exposed to sub-lethal Cu(II) concentrations. In the absence of quinones, the Cu(II)-reduction rate decreased ~70% in respect to the wild-type strain, while this diminution was about 85% in a strain lacking both NDH-2 and quinones. The decrease was ~10% in the absence of only NDH-2. In addition, we observed that quinone deficient strains failed to grow in media containing either excess or deficiency of copper, as we have described for NDH-2 deficient mutants. Thus, the Cu(II)-reduction by E. coli intact cells is mainly due to quinones and to a lesser extent to NDH-2, in a quinone-independent way. To our knowledge, this is the first in vivo demonstration of the involvement of E. coli respiratory components in the Cu(II)-reductase activity which contributes to the metal homeostasis.
authors.affiliation: Departamento Bioquímica de la Nutrición, Instituto Superior de Investigaciones Biológicas (Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de Tucumán), Chacabuco 461, T4000ILI, San Miguel de Tucumán, Tucumán, Argentina.
authors.forename: Sabrina I
authors.initials: SI
authors.lastname: Volentini
authors.forename: Ricardo N
authors.initials: RN
authors.lastname: Farías
authors.forename: Luisa
authors.initials: L
authors.lastname: Rodríguez-Montelongo
authors.forename: Viviana A
authors.initials: VA
authors.lastname: Rapisarda
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D003300:Copper / Q000378:metabolism*; D004579:Electron Transport; D004926:Escherichia coli / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D011809:Quinones / Q000378:metabolism
chemical_list: D011809:Quinones; D003300:Copper; D007501:Iron; D010088:Oxidoreductases; D009245:NADH Dehydrogenase